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RNA interference (RNAi), a phenomenon whereby small double-stranded oligonucleotides can silence gene expression, has been exploited to study protein function in a wide variety of organisms and tissues (see related news item), with one notable exception-neurons. In the 3 September PNAS, currently available online, scientists from Harvard Medical School report that they have successfully used the technique to silence genes in primary cortical neurons from rats.

The two methods most commonly used to introduce small interfering RNAs (siRNAs) into cells were shuttling them across the cell membrane with lipid vectors and transcribing them from transfected DNA. Both have proven either toxic or inefficient in neurons. However, Anna Krichevsky, working in Kenneth Kosik’s lab, used a commercially available transfection agent, called TransMessenger, to introduce siRNAs into these post-mitotic cells. With this method Krichevsky was able to silence expression of microtubule associated protein 2 (MAP2), which is essential for remodeling of the neuronal cytoskeleton. Infected cells not only exhibited a substantial reduction in MAP2 expression but, in addition, a concomitant reduction in filopodia extension, a process that requires a dynamic cytoskeleton.

The suppression was slow, becoming visible only two days after introduction of the interfering RNA. All the same, it indicates that the machinery for RNAi is functional in neurons. The authors suggest that the recently discovered brain micro-RNAs (Lagos-Quintana et al.2002), which are uncannily similar to siRNAs in the manner in which they are processed, may play significant roles in neuronal homeostasis. It will be interesting to see if further study reveals regulatory pathways or mechanisms that will lend themselves to manipulation.—Tom Fagan